In a variety of engine-powered vehicles, monitoring and diagnostic devices are employed to detect the presence of various undesirable operating conditions, such as overheating of the engine, low oil pressure, low fuel, and the like, and indicators are provided to warn the operator of such conditions. These instruments are typically connected to various sensors and switches for monitoring or controlling conditions on the vehicle via a wire harness and/or a communication link. In many applications, these instruments are also connected to electronic control systems, for example electronic engine controls, electronic transmission controls, and the like.
Most prior art systems have included dedicated instruments in which the functions and conditions of the vehicle to be monitored or diagnosed, as well as the particular sensors provided on the vehicle, are identified in advance. Therefore, the instruments are specifically designed for and hence "dedicated" to the monitoring or diagnosing of those particular vehicle functions and conditions in response to signals from pre-identified sensors. Accordingly, such "dedicated" instruments generally cannot be readily modified to accommodate different machines, different sensors and/or different conditions and functions. Rather, such instruments are generally limited to use with a particular vehicle type or model for which the instrument has been designed.
However, it is advantageous for these instruments to be usable in connection with many different machines. Lower costs are achieved and less warehousing space is required if a single instrument can be manufactured which can be used in many different applications. Similarly, service time is reduced if software changes are avoided when an instrument is moved from one machine to another.
Some prior art systems have provided for standardized monitoring systems that are usable in connection with a variety of machines, for example the system shown in U.S. Pat. No. 4,551,801 issued to Sokol on Nov. 5, 1985. While being an improvement over dedicated systems, this monitoring system is still relatively inflexible and requires the addition or subtraction of monitoring modules and the use of decals to indicate the parameters being shown by each display module.
One area of desired flexibility is for each gauge in the instrument to be capable of indicating parameters having a high warning level, for example engine temperature, and also parameters having a low warning level, for example brake fluid pressure. Prior art systems required the use of decals to indicate that the gauge was indicating the level of a parameter having either a high or low warning level and/or the use of a separate warning light to show that the parameter was outside the normal operating range.
To maximize system flexibility, it is advantageous for the instrument to be capable of performing a number of diagnostic functions in addition to displaying parameter values and indicating warning conditions. Today's machines, and particularly large off-highway work vehicles, are becoming increasingly complex in their design thus making it more and more difficult for service personnel to locate defects in machine sensors and systems. This is particularly true of intermittent defects not resulting in a breakdown of a system or the vehicle but which interfere with its operation.
A major frustration when troubleshooting electrical problems on a large work vehicle is caused by intermittent problems. Typically, the operator reports some symptom to a technician and before the technician can get to the machine the problem is no longer present.
If the condition is not present it is helpful for the technician to re-create the fault condition. In many cases the fault condition is caused by a short to ground potential or an open circuit. To recreate these fault conditions, the technician manipulates the wire harnesses or wire connectors to determine the point at which the fault has occurred.
Prior art systems have indicated when fault conditions are present. In connection with such systems, the technician must view a visual display to determine whether the condition is present. In troubleshooting intermittent problems when the fault condition is not currently present, the technician must manipulate wire harnesses and connectors to recreate the fault and thus cause the fault indication to be displayed. When the fault condition is present, the technician must manipulate wire harnesses and connectors and observe whether the manipulations eliminate the fault and thus cause the fault indication to disappear.
In many cases, however, the machine is of sufficient size that the technician must leave the area of the diagnostic tool to recreate the fault condition. Therefore, any visual indicator provided by the diagnostic tool is not visible to the technician. To effectively troubleshoot the electrical system on such a large machine, typically two or more technicians are required and repair expenses are thus greatly increased. Similarly, the vehicle may not be repairable immediately if only a single technician is available.
In addition, these machines typically include switch-type inputs that are either in an open voltage or grounded condition. One of the voltage conditions is defined as a fault condition. In most cases, the fault condition is defined as the open voltage condition thus whenever the wire between the sensor and the display is severed or disconnected, a fault condition is indicated. Similarly, if the switch-type input is connected to a switch-type sensor, the switch-type sensor disconnects the sensor output from ground potential when the sensed parameter exceeds a warning level.
Some prior art systems have illuminated a warning light for each switch-type sensor that is in a fault condition. Each warning light is associated with one of the switch-type sensors and is illuminated when the display input associated with that switch-type sensor is indicating a fault condition. While adequate for many purposes, in other cases it is advantageous to also indicate the pin number of the input associated with the switch-type sensor. Optimally, the technician should be able to determine the pin number of each of the warning lights indicating a fault condition even though there are more than one of such warning lights. This would allow technicians to more readily identify the fault condition and associate the sensor having the fault condition to the relevant connector pin.
While troubleshooting some diagnosable sensor problems, it is sometimes difficult to determine whether a sensor is producing a signal that is truly representative of the actual level of the sensed parameter. This often results in technicians spending time replacing sensors that actually are producing accurate signals which tends to increase the time required, and thus the cost, for repairs.
It is therefore advantageous to determine whether the sensor is producing an accurate signal without replacing the sensor. Since gauges included in the standard operator display do not provide a sufficiently precise readout of the sensed parameter for this purpose, one method of determining the output would be to display the parameter level being reported by the sensor on a digital display and comparing the displayed level to a measurement reported by a test sensor. For example, if the technician is interested in checking the engine coolant temperature sensor, the technician obtains a reference to which to compare the sensor by measuring coolant temperature with a service tool. By comparing the temperatures reported by the vehicle-mounted sensor and the service tool, the technician can determine whether the vehicle-mounted sensor has failed without spending time replacing the sensor.
The present invention is directed to overcoming one or more of the problems set forth above.